Wireless communications systems for mobile subscribers, such as the Global System for Mobile Communications (GSM) cellular system, are well established. In fixed networks it is known to provide subscribers with special services such as Freephone, call forwarding and call barring. These call control services are provided by an intelligent network (IN) which forms an additional layer of the network. By separating some of the call control functions from network switches, services can be developed and applied independently. An intelligent network comprises a number of Service Switching Points (SSPs) which are linked to Service Control Points (SCPs). The SSPs are programmed to recognise `trigger` events, such as a particular pattern of digits (e.g. 0800 for Freephone), and to refer any calls in which a trigger occurs to the SCPs to apply the required service.
It is now intended to provide IN services to mobile subscribers, which requires physical linking of the Public Land Mobile Network (PLMN) to an IN, and establishing protocols to ensure that calls requiring IN services are correctly routed.
Some known arrangements for providing intelligent network services to subscribers of a mobile network are shown in U.S. Pat. No. 5,345,502 (Rothenhofer) and European Patent Application EP 0 630 165 A2 (Alcatel).
International Patent Application WO 95/26114 relates to an intelligent mobile telecommunications network with communication between a logical node of an intelligent network and a logical node of a mobile network.
International Patent Application WO 93/18606 describes an Advanced Intelligent Network (AIN) wireline system which connects to and controls processing of calls to a Personal Communications Service subscriber's wireless handset.
There have been some problems with routing calls between mobile and intelligent networks, which has resulted in calls being incorrectly completed. There is a particular problem where the application of an IN service on the terminating leg of a call requires a call to be completed to the originally called party. The mobile network may repeatedly route the same call to the IN in an infinite loop.
It is an object of the present invention to minimise or overcome these routing problems for calls requiring intelligent network (IN) services.